Based on results from 89-91,92-95; the Regional Coro Program established 12 regional trials to evaluate severallevels of humus (0,2.5,5 and 10 t/ha) at varying levels of Nitrogen (0.75 and 150 kg/ha). Some of these trials have been performed for two or three years at the same site. A negative interaction between net effect of humus and grain yield was found. Response to N was positive at all localities. At all humus levels, yield increased from 0 to 75 kg/ha of N; however, no difference was observed between 75 and 150 kg/ha of N. Ear rot was more related to low N levels than to high humus levels. Results suggest that in order to avoid negative impact of superficial humus on corn grain yield, N must be added at a dose ranging between 100 and 150 kg/ha.